1. Field of the Invention
This invention relates to an improved exhaust-gas heat recovery appliance.
2. Description of Related Art
Exhaust-gas heat recovery appliances are known from the prior art, e.g. U.S. Pat. No. 4,249,375, which proposes a heat exchanger situated before the muffler, in relation to the direction of exhaust-gas flow, of an internal combustion engine. Engine coolant is used to absorb heat from the hot exhaust gases of the internal combustion engine while flowing through the heat exchanger.
To drain off any condensed water that may have formed from cooling exhaust gas, the exhaust-gas zone of the heat exchanger is connected by a drainage line to a region of the exhaust system that is situated further back, allowing any condensed water that does form to flow out of the heat exchanger.
U.S. Pat. No. 4,391,235 has disclosed an exhaust-gas heat recovery appliance which is arranged downstream of an exhaust-gas catalyst, in terms of the flow of exhaust gas, and has an exhaust line with a muffler. Running parallel with the muffler is a bypass line, which can be supplied with exhaust gas via a valve device. In the bypass line there is a heat exchanger, via which heat from the exhaust gas can be fed to engine coolant.
U.S. Pat. No. 4,884,744 is concerned with a heating system for the interior of a motor vehicle with an internal combustion engine. The system has, in addition to a multiplicity of heat exchangers that feed heat from hot engine-operating fluids, e.g. oil or compressed air, to the interior heating system, an exhaust-gas heat exchanger, which is arranged in a bypass line to the main exhaust duct and through which a heating fluid to be warmed flows. Arranged in the bypass line is a throttle valve, which is actuated as a function of the temperature of the heating medium.
U.S. Pat. No. 3,968,649 discloses an exhaust-gas purification system that operates with heat exchangers in the exhaust duct in order to condense some of the pollutants as a liquid that can be separated off or as solids that can be separated off.
U.S. Pat. No. 2,087,411 has likewise disclosed an exhaust-gas condensing device with a condensate separator in which a filter for purifying the condensate is arranged. This appliance is intended to recondense unburnt fuel components in the exhaust gas and feed them back to the engine.
U.S. Pat. No. 5,121,602 has disclosed an exhaust-gas purification appliance that is intended for separating off certain components of the exhaust gas.
With the exhaust-gas heat recovery appliances described above, there is the problem that water in vapor form contained in the exhaust gas condenses due to the removal of heat and is present as a liquid in the exhaust duct.
In the cold part of the year, this liquid can lead to icing in the exhaust duct of the exhaust-gas heat exchanger and, in particular, to icing of exhaust-gas valves arranged in the exhaust duct, thus limiting their operation or even preventing them from operating.
It is the object of the invention to provide an exhaust-gas heat recovery appliance with which the risk of icing is reduced, in particular eliminated. Moreover, the exhaust-gas heat recovery appliance should be of space-saving and economical configuration.